Joint implants, also referred to as joint prostheses, joint prosthetic implants, joint replacements, or prosthetic joints, are long-term surgically implantable devices that are used to partially or totally replace within the musculoskeletal system of a human or an animal diseased or damaged joints, such as, but not limited to, a knee, a hip, a shoulder, an ankle, or an elbow joint. Since their first introduction into clinical practice in the 1960s, joint implants have improved the quality of life of many patients.
Knee arthroplasty is a procedure for replacing components of a knee joint damaged by trauma or disease. During this procedure, a surgeon removes a portion of one or more knee bones forming the knee joint and installs prosthetic components to form the new joint surfaces. In the United States alone, surgeons perform approximately 250,000 total knee arthroplasties (TKAs), or total replacements of a knee joint, annually. Thus, it is highly desirable to improve this popular technique to ensure better restoration of knee joint function and shortening the patient's recovery time.
The human knee joint includes essentially includes four bones. The lower extremity of the femur, or distal femur, attaches by ligaments and a capsule to the proximal tibia. The distal femur contains two rounded oblong eminences, the condyles, separated by an intercondylar notch. The tibia and the femur do not interlock but meet at their ends. The femoral condyles rest on the condyles of the proximal tibia. The fibula, the smaller shin bone, attaches just below the tibia and is parallel to it. The patella, or knee cap, is at the front of the knee, protecting the joint and providing extra leverage. A patellar surface is a smooth shallow articular depression between the femoral condyles at the front. Cartilage lines the surfaces of the knee bones, cushions them, and minimizes friction. Two C-shaped menisci, or meniscal cartilage, lie between the femur and the tibia, serve as pockets for the condyles, and stabilize the knee. Several ligaments connect the knee bones and cover and stabilize the joint. The knee ligaments include the patellar ligament, the medial and lateral collateral ligaments, and the anterior (ACL) and posterior (PCS) cruciate ligaments. Ligaments and cartilage provide the strength needed to support the weight of the upper body and to absorb the impact of exercise and activity. A bursa, or sack, surrounds the knee joints and contains lubricating fluid.
A healthy knee allows the leg to move freely within its range of motion while supporting the upper body and absorbing the impact of its weight during motion. The knee has generally six degrees of motion during dynamic activities: three rotations (flexion/extension angulations, axial rotation along the long axis of a large tubular bone, also referred to as interior/exterior rotation, and varus/valgus angulations); and three translations (anterior/posterior, medial/lateral, and superior/inferior).
A total knee arthroplasty, or TKA, replaces both the femoral component and the tibial component of the damaged or affected by disease knee with artificial components made of synthetic materials, including, but not limited to, metals, ceramics, plastics, or combinations of them. These prosthetic knee components are attached to the bones, and existing ligaments and muscles are used to stabilize the artificial knee. During TKA, after preparing and anesthetizing the patient, the surgeon makes a long incision along the front of the knee and positions the patella to expose the joint. After exposing the ends of the bones, the surgeon removes the damaged tissue and cuts, or resects, the portions of the tibial and femoral bones to prepare the surfaces for installation of the prosthetic components. After preparation of the bones, the knee is tested with the trial components. Ligament balancing, including any necessary surgical release or contraction of the knee ligaments, is performed to ensure proper selection of the prosthetic components and post-operative functioning of the knee. Both anatomic (bone-derived landmarks) and dynamic or kinematic (ligament and bone interactions during the knee movement) data are usually considered when determining surgical cuts and positioning of the prosthetic components. After ligament balancing and proper selection of the components, the surgeon installs and secures the tibial and femoral components. The patella is resurfaced before or after installation of the tibial and femoral component, and a small plastic piece is often placed on the rear side, where it will cover the new joint. After installation of the knee prosthesis, the knee is closed according to conventional surgical procedures. Post-operative rehabilitation starts shortly after the surgery to restore the knee's function.
Improper positioning and misalignment of the prosthetic knee components commonly cause prosthetic knees to fail, leading to revision surgeries. This failure increases the risks associated with knee replacement, especially because many patients requiring prosthetic knee components are elderly and highly prone to the medical complications resulting from multiple surgeries. Also, having to perform revision surgeries greatly increases the medical costs associated with the restoration of the knee function. In order to prevent premature, excessive, or uneven wear of the artificial knee, the surgeon must implant the prosthetic device so that its multiple components articulate at exact angles. Thus, correctly preparing the bone for installation of the prosthetic components by precisely determining and accurately performing all the required bone cuts is vital to the success of TKR.
The surgeons generally rely heavily on their experience to determine where the bone should be cut. They also use various measuring and indexing devices to determine the location of the cut, and various guiding devices, such as, but not limited to, guides, jigs, blocks and templates, to guide the saw blades to accurately resect the bones. After determining the desired position of the cut, the surgeon usually attaches the guiding device to the bone using appropriate fastening mechanisms, including, but not limited to, pins and screws. Attachment to structures already stabilized relative to the bone, such as intramedullary rods, can also be employed.
After stabilizing the guiding device at the bone, the surgeon uses the guiding component of the device to direct the saw blade in the plane of the cut.
To properly prepare femoral surfaces to accept the femoral component of the prosthetic knee, the surgeon needs to accurately determine the position of and perform multiple cuts, including, but not limited to, a transversely directed distal femoral cut, an axially directed anterior femoral cut, an axially directed posterior femoral cut, anterior and posterior chamfer femoral cuts, a trochlear recess cut, or any combination or variation of those. Preparation of the tibia for installation of the tibial component may also involve multiple cuts. Sequentially attaching to the bone and properly positioning a series of cutting guides, each adapted for a specific task, lengthens and complicates the TKR procedure. This problem is particularly pressing in the context of the so-called “minimally invasive surgery” (MIS) techniques.
The term “minimally invasive surgery” generally refers to the surgical techniques that minimize the size of the surgical incision and trauma to tissues. Minimally invasive surgery is generally less intrusive than conventional surgery, thereby shortening both surgical time and recovery time. Minimally invasive TKA techniques are advantageous over conventional TKA techniques by providing, for example, a smaller incision, less soft-tissue exposure, improved collateral ligament balancing, and minimal trauma to the extensor mechanism (see, for example, Bonutti, P.M., et al., Minimal Incision Total Knee Arthroplasty Using the Suspended Leg Technique, Orthopedics, September 2003). To achieve the above goals of MIS, it is necessary to modify the traditional implants and instruments that require long surgical cuts and extensive exposure of the internal knee structures. To make the knee implants and knee arthroplasty instruments, structures, and devices particularly suitable for minimally invasive surgical procedures, it is desirable to decrease their size and the number of components. Cutting systems and devices for MIS are desired that can be installed and adjusted with minimal trauma to the knee's tissues and allow the surgeon to perform the cuts quickly and efficiently without compromising the accuracy of the resection. Also desired are cutting systems and devices that minimize the number of the surgical steps required to accurately cut the bones in preparation for installation of the prosthetic knees.
Another recent development in TKA is computer-assisted surgical systems that use various imaging and tracking devices and combine the image information with computer algorithms to track the position of the patient's leg, the implant, and the surgical instruments and make highly individualized recommendations on the most optimal surgical cuts and prosthetic component selection and positioning. Several providers have developed and marketed imaging systems based on CT scans and/or MRI data or on digitized points on the anatomy. Other systems align preoperative CT scans, MRIs, or other images with intraoperative patient positions. A preoperative planning system allows the surgeon to select reference points and to determine the final implant position. Intraoperatively, the system calibrates the patient position to that preoperative plan, such as using a “point cloud” technique, and can use a robot to make femoral and tibial preparations. Other systems use position and/or orientation tracking sensors, such as infrared sensors acting stereoscopically or otherwise, to track positions of body parts, surgery-related items such as implements, instrumentation, trial prosthetics, prosthetic components, and virtual constructs or references such as rotational axes which have been calculated and stored based on designation of bone landmarks. Processing capability such as any desired form of computer functionality, whether standalone, networked, or otherwise, takes into account the position and orientation information as to various items in the position sensing field (which may correspond generally or specifically to all or portions or more than all of the surgical field) based on sensed position and orientation of their associated fiducials or based on stored position and/or orientation information. The processing functionality correlates this position and orientation information for each object with stored information regarding the items, such as a computerized fluoroscopic imaged file of a femur or tibia, a wire frame data file for rendering a representation of an instrumentation component, trial prosthesis or actual prosthesis, or a computer generated file relating to a rotational axis or other virtual construct or reference. The processing functionality then displays position and orientation of these objects on a screen or monitor, or otherwise. The surgeon may navigate tools, instrumentation, trial prostheses, actual prostheses and other items relative to bones and other body parts to perform TKAs more accurately, efficiently, and with better alignment and stability.
With the introduction of the computer-assisted surgical systems, adjustable systems for cutting the bone during TKR became particularly desired. Although some providers developed adjustable cutting blocks, their adjustment capabilities were generally limited to setting a parameter, such as the varus/valgus angle, prior to installation of the cutting block The cutting systems capable of being adjusted continuously during surgery were not desirable, because the surgeon was not able to follow the position of the installed cutting block after adjustment. Once the computer-aided systems and processes became available that can provide useful data throughout TKR surgery on predicted or actual position and orientation of body parts, surgically related items, implants, and virtual constructs for use in navigation, assessment, and otherwise performing surgery or other operations, cutting systems became particularly desirable whose position can be continually adjusted after taking into account the feedback from the computer functionality. Additionally, the known adjustable cutting systems are not suitable for minimally invasive surgery, because they are generally too large to be placed in a small incision, too cumbersome to use, and require additional mechanical referencing devices for proper positioning and adjustment.
Thus, multifunctional systems for guiding bone cuts during TKR are needed that are particularly well adapted for use in minimally invasive surgery, computer-assisted surgery, or both. To this end, cutting systems or devices are needed that are smaller than conventional cutting systems and devices, and allow the surgeon to minimize the size of the surgical incision and tissue damage, thereby reducing the surgical repairs and shortening the recovery time. Cutting systems and devices are needed that minimize damage the bone during installation. Cutting systems and devices are needed that can be positioned and installed at the bone without the encumbrances of mechanical referencing devices. Further, cutting systems and devices are needed whose position can be precisely controlled before and after installation so that it is possible to place them accurately in the desired location suggested by the navigation system. Also, there is an unrealized need in cutting systems and devices with multiple adjustment parameters. Particularly, systems and devices are desired that are adjustable in multiple angles of rotation and multiple translations, but miniature enough to be useful for minimal invasive surgery, thereby reducing patient visit time and costs, and potential of infection. In general, surgical cutting guides are needed for use in TKA that are easy to use and manufacture, minimize tissue damage, simplify surgical procedures, are robust, can withstand multiple surgeries and required sterilization treatments, are versatile, allow for faster healing with fewer complications, require less post-surgical immobilization, are simple to use so as to require less operator training, and also less costly to produce and operate.